000
FXUS66 KOTX 092313
AFDOTX
Area Forecast Discussion
National Weather Service Spokane WA
313 PM PST Fri Dec 9 2016
.SYNOPSIS...
Periods of light snow will continue through the weekend and into
early next week. Brisk dry north winds are expected Monday down
the Okanogan Valley the will spread out over the western basin.
Temperatures will become very cold by Tuesday and will continue
through next week. Many areas will see overnight temperatures fall
into the single digits with some locations seeing temperatures
below zero for early to mid week.
&&
.DISCUSSION...
Tonight: More snow. The warm front will take another surge over
the forecast area with bands of light snow continuing through the
evening. The main moisture tap lies across Oregon, but satellite
showed an arch northward into southeast Washington. Isotropic lift
will steadily increase and low levels warm. An upper level
shortwave ripples through the region overnight coupled with a weak
cold frontal passage. Precipitation will taper off from west to
east late tonight.
Snow: Snow will be the main precipitation type, but how much is
the big question? Qpf looks light to moderate, peaking during the
overnight hours. And this will translate to the snow amounts.
Snow ratios will range quite a bit across the region, dropping
down to a mere 6:1 in the LC Valley overnight while the mountains
and higher valleys near the Canadian border may see fluffy snow of
20:1. This is all dependent on temperature profile.
Best estimates are 1 to 3 inches in the valleys of the Okanogan
Highlands, northeast Washington and north Idaho, Spokane/Coeur
d`Alene area and Palouse. Up to 2 inches from Okanogan Valley to
Wenatchee to the Columbia Basin. 6 inches or more in the high
Cascade valleys and mountains. Higher amounts will be focused near
the Cascade crest and Bitteroots.
Wintry Mix: Warmer air will creep around the Blue mountains into
the southern Palouse and may lead to pockets of freezing rain or
sleet this evening.
Travel Impacts: Based on the current snow trends, roads and their
fluctuating temperatures, opted to host Winter weather advisories
for many areas across the northeast Washington and north Idaho.
Some road surfaces are wet and will most likely see freezing
conditions this evening during the evening commute as more snow
arrives. This is in addition to the pockets of freezing rain to
the south. Icy and snow covered roads increase the impacts for the
night. /rfox
Saturday through Sunday Night: Periods of light snow will
continue through the weekend. Saturday morning light snow will
move out of the area with the best chance of snow in the Cascade
mountains and mountains of the central ID Panhandle. Saturday
night the low pressure system off Vancouver Island will weaken and
move inland. This will provide another chance of widespread light
snow to the region. Then Sunday and Sunday night the influence of
the trough remains in the area with weak weather disturbances
keeping the threat of snow for much of the region.
*Snow amounts:
Saturday: Locations like Wenatchee...Waterville
Plateau and the Columbia Basin will see near 0. Across extreme
eastern WA it will range from a T to a half an inch. The valleys
of north ID and east slope Cascades will see a half an inch to a
little over an inch. The highest amounts will be along the
Cascade crest and the mountains of Shoshone Co where they would
see 1 to 3 inches with locally higher amounts possible.
Saturday evening through early Monday morning: Once again
Wenatchee, the Waterville Plateau and Moses Lake area will likely
see near 0 for snowfall. As you head east towards Ritzville they
could see around 2 inches. Northern WA from the Okanogan Valley
east towards the ID border, they could see anywhere from a half
inch in the Okanogan Valley to 1 to 3 inches in the valleys to the
east...with 4 to 6 inches in the mountains near the ID border.
The Cascade valleys could see 3 to 6 inches with over a foot along
the crest. The Spokane/COE area will see anywhere from 2-5 inches
of snow...with the higher amounts likely in ID. The Palouse could
see 3-6 inches of snow with locally higher amounts in ID. From
the Blues east into the Camas Prairie...will see near 0 portions
of the LC Valley and Snake River area with perhaps up to an inch
in Lewiston. The higher terrain will see 3 to 6 inches. The ID
Panhandle will see 5 to 8 inches in the valleys and 8 to 16 inches
in the mountains. Those higher amounts will likely be in Shoshone
County.
So...needless to say unsettled through the weekend. Snow
accumulations will generally be light each 12-18 hr period, but it
will be persistent...so by the end of the weekend there should be
some decent accumulations of snow. Winter highlights may be
needed, but want to let the highlights for tonight play out before
we issue more. /Nisbet
Monday through Friday: The big story through next week will likely
be the cold temperatures. There is some uncertainty how this week
plays out exactly and at this time...the forecast continues to
favor a blend of the GFS/Canadian/GEFS/EC Ens Mean. The EC
deterministic is trending this direction but does offer some
differences in regards to how cold...timing of the cold...and
potential for light snow across my far southern CWA boundary.
As it stands now...Monday will be the last day of light snow before drier
and colder air settles in. The main threat for light snow Monday
will be along and south of Hwy 2. The remnants of the offshore low
will track through the area initiating a weak southerly push.
Meanwhile...the first push of Canadian air will spill south. These
boundaries look to collide across Ern WA and N ID near or south
of the Hwy2 corridor Monday afternoon delivering once last chance
for snow showers. Otherwise...most snow shower activity will focus
in the mountains of the lower Idaho Panhandle, Camas Prairie, and
Cascade Crest in response to favored w/nw flow. Accumulations on
a whole will generally be light with the potential for 0.5-2.0".
The focus following the snow chances Monday afternoon will be breezy
winds and cold temperatures. Gusty N winds will usher the first
push of polar air with 850mb temperatures expected to cool back
into the lower teens where they will remain through much of the
week. Thinking the brisk northerly winds Monday night will keep
temperatures from plummeting Tuesday morning however each
Wednesday and Thursday morning`s have the potential for maximum
radiational cooling under clear skies, light winds, and fresh snow
pack allowing temperatures to sink into the single digits, some
locations below zero, some perhaps lower teens. If we are able to
radiate into these values...the combination of the time of year,
lack of sun, and light winds suggest afternoon highs will struggle
to warm more than 10 degrees from the morning low which may yield
highs in the upper single digits to teens...again pending how
cold each morning becomes. There are many factors that could alter
this forecast such as more fog or stratus, passing midlevel cloud
deck, slightly higher puffs of winds, or even if the
deterministic EC were to verify. However, even the EC is cold, it
would just be delayed until later in the week. /sb
&&
.AVIATION...
00Z TAFS: The next band of precipitation is moving into the region
from the southwest. Anticipate mainly MVFR cigs and light snow
across much of the region. As snow intensities increase,
anticipate cigs to lower to IFR and occasional MVFR vsbys. There
some indication of a brief period of FZRA late tonight into early
Sat morning for the KPUW/KLWS area. Think the depth of the cold
air is sufficient to keep it mostly as snow. Anticipate improving
cig/vsbys after 15z from south to north as the warm front pushes
north and a cold front moves through the region. There are
indications that more VFR conditions are possible. /rfox.
&&
.PRELIMINARY POINT TEMPS/POPS...
Spokane 21 30 28 34 24 27 / 80 20 80 40 50 40
Coeur d`Alene 19 31 28 35 25 29 / 90 70 80 70 50 40
Pullman 27 32 29 35 28 30 / 80 70 80 70 70 60
Lewiston 28 37 31 40 29 34 / 80 30 60 50 50 40
Colville 21 32 28 35 23 29 / 90 30 70 30 20 10
Sandpoint 18 31 29 34 27 29 / 90 60 80 60 30 30
Kellogg 21 30 28 32 26 28 / 90 90 100 90 90 70
Moses Lake 20 30 25 35 22 28 / 60 10 30 10 10 30
Wenatchee 21 30 26 34 26 30 / 80 10 30 10 10 30
Omak 19 29 25 33 21 26 / 70 20 60 10 10 10
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 10 AM PST Saturday for Central
Panhandle Mountains-Northern Panhandle.
Winter Weather Advisory until 4 AM PST Saturday for Coeur
d`Alene Area-Idaho Palouse.
WA...Winter Weather Advisory until 10 AM PST Saturday for Northeast
Mountains.
Winter Weather Advisory until 4 AM PST Saturday for Okanogan
Highlands-Spokane Area-Washington Palouse.
Winter Weather Advisory until 4 PM PST Saturday for East Slopes
Northern Cascades.
&&
$$